Sigma DC HSM Lenses

By sorcadmin  Posted: Nov 27, 2007

17-70mm

18-50mm

Both lenses are designated as "macro", which in common terms means
close focusing and not 1:1 reproduction ratio; here it's more like 1:2.3.
But given that you can focus as close as about 8 in. throughout the focal length
range you can get some great depth of field effects utilizing the widest setting
and fast f/2.8 maximum aperture/f/22 minimum aperture on both. Of course, having
a constant max aperture of f/2.8 helps in many more situations, which the extra
$100 or so for the 18-50mm justifies.

Both lenses have multi-coated optics that delivered snappy images even under
lighting conditions rife with flare potential. They also offer internal focusing,
which means that although the lens barrel extends with zooming the act of focusing
does not rotate the lens itself, useful when using polarizing filters. While
f/2.8 max aperture necessitates a fairly broad front element (72mm filter size)
the weight on both lenses does not add to the feathery light Nikon D40 on which
I used them.

This is not a shootout test between the two lenses, so comparatives don't
count, but I certainly wouldn't think of having both lenses in my kit.
You do lose about a stop and a half with the variable aperture zoom and go just
slightly wider. The question is: do you need a fast, constant aperture or can
you live with a 1.5 stop loss when you zoom in? That's a question only
you, and your style of shooting can answer.

Both Sigma lenses delivered crisp images under various lighting conditions
during two weeks in the brilliant fall light of Northern New Mexico. And any
lens that translates those edges and silvery light faithfully is always welcome
in my camera bag. AF operation was swift and accurate, and performed flawlessly
with each Nikon AF mode. It was also silent and lacked any "chatter"
that some zooms exhibit.

These shots were made with the 17-70mm lens. With strong backlight
and specular highlights and angular side lighting there is always
a potential for flare and ghosting, something multi-coating diminishes
to a great extent. In addition, the crisp, nice contrast of the
lens brings out all the detail in the fall scene right after the
first season's snow.

Given that Nikon continues on the AF-S only course for their beginner and
perhaps even advanced amateur DSLRs (and given Nikon's recent lens announcements
this seems likely) and that perhaps even other makers will follow this course,
Sigma's HSM lens offerings should grow. Given what these lenses deliver
they are an excellent option for those looking to add to their kit. Prices shown
are MSRP; you might find lower prices when you shop.